1. Field of the Invention
The present invention relates to a wafer for a heavy metal monitor and a method for monitoring an amount of heavy metal contamination in a wafer, which is capable of measuring the degree of heavy metal contamination with good accuracy, even in a manufacturing process in which a large-diameter wafer of 8 inches or 12 inches and over is being processed.
2. Description of the Related Art
In the past, in a process for manufacturing a semiconductor, heavy metal contamination, which causes a deterioration of the characteristics of a semiconductor, such as with regard to leakage, was measured and monitored by a minority carrier lifetime measurement apparatus which made use of the xcexc-PCD method (microwave photoconductive decay).
In particular, because it was advantageous to have the wafer that is used for this monitoring be the same size as the wafer being processed, as the size of silicon wafers grew, in order to achieve rigidity with respect to stress, the thickness of the wafer grew large, the result being that the apparent lifetime became long, this hindering measurement with good accuracy.
FIG. 3 shows the method for monitoring heavy metal in the past. This wafer is subjected to thermal oxidation at a temperature in the range from 900xc2x0 C. to 1000xc2x0 C. in an atmosphere of O2 or in an atmosphere of N2 and O2, thereby achieving thermal treating for the purpose of preventing surface recombination.
However, a metal such as titanium, which has a low diffusion coefficient, is introduced into the oxide film during thermal treating, in which case there is a further deterioration of the measurement accuracy.
Accordingly, it is an object of the present invention to improve on the drawbacks of the prior as noted above, by providing a novel wafer which enables measurement of the amount of heavy metal contamination with good accuracy, even in a process of manufacturing a large-diameter wafer, and a further object to provide a method for monitoring an amount of heavy metal contamination in a wafer.
Another object of the present invention is to provide a novel wafer for monitoring heavy metal contamination that is capable of measuring of the amount of metal contamination with good accuracy, while suppressing the measurement error that is introduced by the introduction of a metal such as titanium, which has a low diffusion coefficient, into the oxide film.
In order to achieve the above-noted objects, the present invention adopts the following basic technical constitution.
The aspect of the present invention is a method for monitoring the amount of the heavy metal contamination on a wafer, this method comprising the steps of;
setting a wafer for monitoring an amount of heavy metal contamination in a prescribed monitoring place,
performing thermal treatment to the wafer at a temperature in the range from 1150xc2x0 C. to 1350xc2x0 C. in an atmosphere of O2+He or an atmosphere of H2+He,
performing thermal treatment to the wafer at a temperature in the range from 900xc2x0 C. to 1000xc2x0 C. in an atmosphere of N2+O2 or an atmosphere of O2, and measuring an amount of heavy metal contamination in the wafer.
In a method for monitoring the amount of heavy metal contamination on a wafer, by measuring minority carriers lifetime, this method having a step of thermal treatment at a temperature in the range from 1150xc2x0 C. to 1350xc2x0 C. in an inert light element gas atmosphere of O2+He or an atmosphere of H2, +He, and a step of thermal treatment at a temperature in the range from 900xc2x0 C. to 1000xc2x0 C. in an atmosphere of N2+O2 or an atmosphere of O2, and by means of these steps, it is possible to eliminate the measurement error that occurs because of the inclusion of a metal such as titanium, which has a low diffusion coefficient, into the oxide film during thermal treating, thereby resulting in the achievement of good measurement accuracy.